This is a difficult case to analyze because there is no real evidence. There are anecdotal claims made by sources that are opposed to GM crops. There are few scientific observations to explain why the sheep died. What we do know if that they appeared to die of pesticide poisoning and not from Bt exposure. Animals have been fed large amounts Bt in laboratory studies without any ill effects. One ray of sunshine is that use of Bt cotton should allow an 80-95 percent reduction in chemical pesticide application that will be safer for the farmers, their villages and their sheep. It is unreasonable for Jeffrey Smith to repeat such poorly documented cases.

Sheep died while grazing in cotton fields before Bt cotton. It is a fact that there are reports of sheep having died from grazing in Bt-cotton fields. These reports documented by Smith come from self-described anti-GM groups. These sources Smith cites for the most part only point fingers and ask for more investigation of the phenomenon. Unfortunately for poor farmers, sheep have been dying in fields long before Bt cotton was introduced and that they have died from grazing fields where Bt cotton was not grown. There are well-researched explanations for death of grazing sheep that do not involve Bt-cotton. Intoxication of sheep with plant derived chemicals such as cyanide, oxalate, or nitrate, or with forage contaminants such as pesticides or fungal toxins is moderately common (e.g. Mayland and others 1995, Wang and Provenza 1996).

The sheep appear to have died from acute toxicity. Veterinarians who examined some of the dead sheep said that they showed symptoms of exposure to a toxic agent (Smith says this).

Pesticide or nitrate poisoning are likely explanations. Veterinarians concluded the most likely cause was pesticide poisoning. They recognized pathological signs of acute toxicity. They could not rule out nitrate or gossypol (a natural toxic ingredient of cotton plants) as toxic agents. Other investigations showed that high nitrate levels in the cotton might explain the deaths (Karihaloo and Kumar 2009).

Bt has a long history of safe use and is non-toxic to mammals. Bt is completely non-toxic to animals and no veterinarian or toxicologist has suggested that Bt cotton is responsible for the deaths (Siegel 2001, Betz and others 2000, Whelon and Wingerd 2003)

Bt cotton is widespread and reports of problems are not. Half of the cotton grown in the world is Bt cotton. No similar reports have come from the over 10 million farmers who plant Bt-cotton (www.isaaa.org; Brookes and Barfoot, 2007). The dramatic reduction in pesticide application associated with adoption of Bt cotton may further reduce the widespread incidence of human and animal pesticide poisonings—a major benefit of insect protected crops is that they require little or no pesticides.